Investigating the Effect of Different Subflow MTUs on MPTCP Throughput

Abstract

Abstract Multipath TCP (MPTCP) is an extension of the traditional Transmission Control Protocol (TCP) that enables simultaneous use of multiple network paths between two endpoints, offering improved resilience, throughput, and resource utilization. While existing MPTCP implementations perform well in homogeneous environments, their behavior in heterogeneous networks, particularly when subflows have different Path Maximum Transmission Units (MTUs) remains underexplored. This research investigates the impact of varying subflow MTUs on MPTCP throughput using a controlled emulation environment. Experimental analysis reveals that the default Linux MPTCP implementation fails to utilize subflows with smaller MTUs effectively, primarily due to limitations in the Path MTU Discovery (PMTUD) mechanism and a unified Maximum Segment Size (MSS) approach. Kernel-level modifications were introduced to enable MTU probing on a per-subflow basis, allowing dynamic MSS adjustment and improved subflow utilization. Results demonstrate a notable improvement in throughput and path diversity post-modification, highlighting the importance of MTU-aware scheduling and adaptive probing techniques. The findings suggest potential directions for enhancing MPTCP performance in heterogeneous environments and contribute to the ongoing development of more robust multipath communication protocols.